Our lab is broadly interested in the mechanisms by which both somatic and embryonic stem cells acquire and maintain developmental potency. We are also exploring how deregulation of these mechanisms can contribute to oncogenic transformation and tumorigenesis, and how we can learn to manipulate these mechanisms for application in disease modeling and regenerative medicine

Nuclear reprogramming during iPS cell generation

Recent advances in the field of epigenetic reprogramming have changed what was previously a highly controversial and technically challenging experimental system (nuclear transfer, or cloning) into a simple and robust methodology (iPS cell generation). The generation of induced pluripotent stem cells (iPSCs) can be accomplished simply by ectopic expression of four transcription factors, Oct4, Sox2, Klf4, and c-Myc, in somatic cells. This process reverts the somatic genome into a pluripotent epigenetic state that is indistinguishable from that of an embryonic stem cell. We have previously shown that this process is relatively efficient and largely independent of the origin of the somatic donor cell. It is also known that this process is accompanied by dramatic changes in the gene expression program and chromatin organization of the somatic nucleus. Using gain and loss of function approaches in genetically modified primary somatic cells harboring both drug-inducible reprogramming alleles and pluripotency reporter alleles coupled with genomic analyses, we are investigating the influence of chromatin-modifying proteins and nuclear organization on the dynamics of the epigenetic reprogramming process.

In the mammalian soma, tissue-specific stem cells capable of maintaining organization and function during homeostasis and of regenerating damaged tissue upon insult are commonly thought to exist in a state of multipotency (the ability to generate any cell type of that particular tissue, in contrast to the pluripotent state embodied by embryonic stem cells capable of generating all cell types of the mammalian organism). We have recently demonstrated that the genetic pathway governing pluripotency in embryonic stem cells does not contribute to somatic stem cell potency. Therefore, we have performed several screens aimed at identifying factors that may govern somatic stem cell multipotency in a broad range of tissues and have identified the Msi family of RNA binding proteins as attractive candidates. Msi proteins are expressed in putative somatic stem cell compartments, are frequently found to be overexpressed in advanced cancers, and are known to govern asymmetric cell division in Drosophila melanogaster (a process thought to maintain the somatic stem cell niche in mammals). Using mouse genetic approaches integrated with human patient sample data, we have recently demonstrated that human MSI2 contributes to maintaining the stem cell state in hematopoietic stem cells (HSCs) and acts as a cooperating oncogene in chronic and acute myelogenous leukemias by conferring a stem cell-like state to the transformed cells. We are currently pursuing the role of Msi proteins in epithelial stem cell compartments using tissue-specific gene ablation and drug-inducible gene activation. We are relating the effects of Msi proteins on stem cell maintenance and oncogenic transformation to their RNA binding capacity using CLIP-Seq analysis and will ultimately determine how these functions affect asymmetric stem cell division using both mouse and cell culture models.

Gaining an understanding of the mechanisms that govern somatic stem cell potency and how these mechanisms are linked to oncogenic transformation will provide the impetus for harnessing these pathways for the generation of potential therapeutic cell types in vitro and may enable more effective, targeted approaches for intervention during the progression of various cancers.